The time-scaled logic diagram: seeing the driving path, not just the bars
A Gantt chart shows you when every activity happens. It is hopeless at showing the one thing every delay conversation turns on — the chain of work that actually drives the finish date. The time-scaled logic diagram (TSLD) exists to answer that question, and once you have read one you will wonder why it is not the default.
The problem the Gantt can't solve
Open a 2,000-line programme as a Gantt and ask a simple question: which activities are driving the completion date, and how do they hand off to each other? The answer is in there — but it is scattered down hundreds of rows, sorted by WBS, with the critical chain hopping from row 40 to row 900 to row 220. You can filter to "critical only" and still be left scrolling a column of bars with no sense of how they connect. The Gantt is organised for browsing the whole schedule, not for reading one path through it.
This is exactly the gap Primavera's P6 Visualizer set out to fill, and the time-scaled logic diagram is its signature view. The idea is simple and, in hindsight, obvious: instead of one activity per row, put a whole chain of logically-connected activities on the same row, laid out left-to-right against a real timescale, with the relationships drawn inline between them. An entire driving path then reads as a single horizontal line.
How a TSLD is built
The construction is mechanical once you have a critical path. Trace the driving (longest) path back from the latest-finishing activity — each activity, then the predecessor that actually controls its start, hop by hop, to the data date. That ordered chain becomes one band. Within the band, activities are placed left-to-right by date on a single row; where two genuinely run in parallel, the later one drops to a sub-row so nothing overlaps. The relationships between consecutive activities are drawn as short elbow connectors, colour-coded by type, so you can see whether the hand-off is a clean finish-to-start or something looser. (If the difference between finish-to-start and the rest is hazy, our piece on leads, lags and logic density is the companion read.)
Most driving paths are near-sequential, so a band is usually one or two rows — the whole point is density. Beneath the critical band you can stack the near-critical paths (second-longest, third-longest), each on its own band, so you see not just today's driver but the chains poised to become critical if the leader recovers.
What it is good for
Three jobs, mainly. Communicating the spine of a programme to people who will never open P6 — a director sees the critical chain over time in one picture instead of a 40-page bar-chart PDF. Spotting the near-critical threat — the second and third paths are where tomorrow's delay comes from, and they are invisible in a critical-only Gantt filter. And delay storytelling — when you need to show how the driving path runs, or how it migrated between two revisions, a side-by-side TSLD makes the argument in a way a table of float values never will. That migration view pairs naturally with the question of which "critical path" you even mean, since a TSLD is usually built on the longest (driving) path rather than the total-float definition.
| Question | Gantt | TSLD |
|---|---|---|
| When does activity X happen? | Excellent | Fine |
| What is the full scope / all activities? | Excellent | Not its job |
| Which chain drives the finish? | Poor — scattered | Excellent |
| What's about to become critical? | Poor | Good (near-critical bands) |
| How did the driving path move vs baseline? | Very hard | Good (compare mode) |
What it is not
A TSLD is a lens on the critical and near-critical paths, not a replacement for the Gantt. It deliberately does not show every activity — drawing the whole network as condensed chains just produces a worse, more tangled Gantt. Use it to read the driving logic; use the Gantt to browse the programme and the columns that matter.
Why it has been locked away — until now
For two decades the TSLD lived inside P6 Visualizer, which means it required a Primavera licence and the patience to drive Visualizer's layout machinery. Reviewers, quantity surveyors, project directors and expert witnesses — exactly the people who most need to see the driving path — usually don't have that. The maths behind it isn't heavy (it's a longest-path trace plus a row-packing layout), so there is no good reason it should be confined to desktop Primavera. Bringing it into the browser, alongside the quality checks and baseline comparison, is one of those features that feels overdue the moment you use it.
Key takeaways
- A Gantt scatters the critical path down hundreds of rows; a TSLD condenses the driving chain onto one time-scaled band with the logic drawn inline.
- Stack near-critical bands beneath it to see the chains about to become critical — invisible in a critical-only Gantt filter.
- It's a lens, not a Gantt replacement: it shows the driving path, not every activity.
- Only as honest as the network — fix open ends and constraints (the 14-point check) before trusting the path it traces.
- Historically locked inside P6 Visualizer; the underlying maths is light enough to run in a browser.
See your driving path as a logic diagram
Drop a P6 XER or MS Project file in your browser, open the Schedule tab and switch on ⛓ Logic (TSLD) — the critical chain, near-critical bands and inline logic, with nothing uploaded.